OLED Pixel Circuit with Capacitor for Black State Light Leakage

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Solution Overview

Problem

Existing OLED pixel circuits face issues with electric leakage and unstable threshold voltage, leading to light leakage in the black state, affecting contrast ratio and service life due to fabrication technique fluctuations and signal coupling.

Innovation Solution

A pixel circuit design incorporating a driving control module, a first light emitting control module, a light emitting device, and a first capacitor, where the first capacitor controls the light emitting device to be in reverse cut-off when an invalid light emitting control signal transitions to a valid signal and the driving current is below a preset gray-scale value, preventing light emission in the black state and reducing device aging.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If a conventional OLED pixel circuit is used, then the display can show images, but electric leakage and unstable threshold voltage cause light leakage in the black state

Engineering Contradiction:

Improveblack state brightnessVSAvoidthreshold voltage stability

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The pixel circuit is divided into multiple functional modules: driving control module (with drive transistor and compensation capacitor), light emitting control module (with light emitting control transistor), and holding module (with first capacitor). This segmentation allows each module to independently address specific issues - the compensation capacitor stabilizes threshold voltage while the light emitting control transistor prevents light leakage, resolving the contradiction between black state brightness and threshold voltage stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The light emitting control transistor acts as an intermediary between the driving control module and the light emitting device. It controls the light emitting state based on the light emitting control signal, preventing direct coupling between driving signals and the light emitting device that would cause instability and light leakage in the black state.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If the light emitting device is continuously driven, then display functionality is maintained, but device aging accelerates

Engineering Contradiction:

Improvedisplay operation continuityVSAvoiddevice service life

Core Design Contradiction:

ProductivityVSDuration of action of stationary object

Solution Approach 1:

The light emitting control signal is periodically switched between valid and invalid states. During invalid periods, the light emitting device is turned off or placed in reverse cut-off mode, allowing it to rest and recover. This periodic operation maintains display functionality while reducing cumulative stress and aging of the light emitting device.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The first capacitor is configured to control the light emitting device to be in reverse cut-off mode under specific conditions (when light emitting control signal is invalid and driving current is below threshold). This preliminary protective action prevents forward conduction and potential damage before aging can occur, extending device service life while maintaining operational continuity.

Inventive Principle:

Principle #9Preliminary anti-action

3Ease of manufacture

If fabrication techniques have fluctuations, then manufacturing cost is reduced, but electric leakage and threshold voltage instability increase

Engineering Contradiction:

Improvefabrication toleranceVSAvoidelectric leakage

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The compensation capacitor and light emitting control transistor are designed as protective elements that anticipate and compensate for fabrication variations. The compensation capacitor stores threshold voltage information to counteract drift, while the light emitting control transistor provides an additional control layer that prevents electric leakage even when transistor parameters vary due to fabrication fluctuations.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

4Device complexity

If signal coupling occurs between control signals, then circuit complexity is reduced, but light leakage in black state increases

Engineering Contradiction:

Improvesignal couplingVSAvoidblack state light leakage

Core Design Contradiction:

Device complexityVSIllumination intensity

Solution Approach 1:

The light emitting control transistor serves as an intermediary that isolates the light emitting device from direct coupling with driving signals. It responds only to the dedicated light emitting control signal, preventing unwanted signal coupling while maintaining circuit simplicity. The transistor's gate is controlled by a separate signal line that directly controls light emission without interfering with driving waveforms.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12118933B2Pixel circuit, driving method, electroluminescent display panel and display apparatus

Publication Date: 2024.10.15 CHENGDU BOE OPTOELECTRONICS TECH CO LTD

AI summary

Disclosed are a pixel circuit, a driving method, an electroluminescent display panel and a display apparatus. The pixel circuit includes: a driving control module, a first light emitting control module, a light emitting device and a first capacitor; where the first light emitting control module is coupled between the driving control module and a first electrode of the light emitting device; and the first capacitor is coupled between the light emitting control end and the first electrode of the light emitting device.